streamline skvm errors

store() returns a success bool only because it can, because it wasn't
going to return any sort of skvm::Value anyway.  But it should never
fail given a well-formed skvm::PixelFormat, e.g. one from
SkColorType_to_PixelFormat.  So move the "error handling" inside, really
just asserting/assuming it doesn't fail.

And similarly, skvm::SkColorType_to_PixelFormat() can no longer fail, so
have it return the skvm::PixelFormat directly instead of the bool I used
to stage things back when building this out.

Change-Id: I6dc3b6da32cdaaef377fe59b8c94846e902841ee
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/367796
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/src/shaders/SkImageShader.cpp b/src/shaders/SkImageShader.cpp
index 6a0c7cf..88f5aa2 100755
--- a/src/shaders/SkImageShader.cpp
+++ b/src/shaders/SkImageShader.cpp
@@ -879,15 +879,6 @@
 
     skvm::Coord upperLocal = SkShaderBase::ApplyMatrix(p, upperInv, origLocal, uniforms);
 
-    // All existing SkColorTypes pass these checks.  We'd only fail here adding new ones.
-    skvm::PixelFormat unused;
-    if (true  && !SkColorType_to_PixelFormat(upper.colorType(), &unused)) {
-        return {};
-    }
-    if (lower && !SkColorType_to_PixelFormat(lower->colorType(), &unused)) {
-        return {};
-    }
-
     // We can exploit image opacity to skip work unpacking alpha channels.
     const bool input_is_opaque = SkAlphaTypeIsOpaque(upper.alphaType())
                               || SkColorTypeIsAlwaysOpaque(upper.colorType());
@@ -924,8 +915,7 @@
     };
 
     auto setup_uniforms = [&](const SkPixmap& pm) -> Uniforms {
-        skvm::PixelFormat pixelFormat;
-        SkAssertResult(SkColorType_to_PixelFormat(pm.colorType(), &pixelFormat));
+        skvm::PixelFormat pixelFormat = skvm::SkColorType_to_PixelFormat(pm.colorType());
         return {
             p->uniformF(uniforms->pushF(     pm.width())),
             p->uniformF(uniforms->pushF(1.0f/pm.width())), // iff tileX == kRepeat